In the prior art, the frequency band of the Universal Mobile Telecommunications System (Universal Mobile Telecommunications System, UMTS for short) is 5 MHz wide. A network transmits and receives data on the same uplink and downlink bandwidth, and user equipment (User Equipment, UE for short) also transmits and receives data on the same bandwidth.
A narrow-band UMTS system has relatively high spectral efficiency. For the uplink, if a 5 MHz band is divided into multiple subcarriers, uplink interference between UEs on different subcarriers will decrease. Therefore, a high uplink throughput is obtained when the UEs perform uplink transmission in a narrow-band system.
When the downlink band is 5 MHz, and the 5 MHz uplink band is divided into two subcarriers, the length of a downlink sub-frame is half that of an uplink subcarrier. When downlink carrier bandwidth is N times uplink carrier bandwidth, a length of a downlink sub-frame or transmission time interval is 1/N of a length of an uplink sub-frame or transmission time interval. For timing of all uplink channels of N uplink carriers, reference is made to a channel of a same downlink carrier.
However, narrow bandwidth makes it difficult to perform uplink feedback in a scenario in which downlink bandwidth is different from uplink bandwidth.
In addition, in other systems in which an uplink transmission time interval (such as a length of a sub-frame) is greater than a downlink transmission time interval (such as a length of a sub-frame), the same uplink feedback issue exists.